lowhurst



Feb. 2, 1960 H LOWHURST 2,923,897

DUO-MODE WAVE ENERGY FEED Filed Oct. 29, 1956 INVENTOR, HARVEY G. LOWHURST ATTORNEY United States Patent 9 d 2 2,923,897 DUO-MODE WAVE ENERGY FEED Ha rvyL G;:LnwliurstfLos Kngeles, Califi, assignor to -:Hughes Aircraft Cdmpa'ri ,CMverICity, Califl, a cor- 'por'ation ofDelaWareL a Application ctober29, 1956, Serialflflo. 618,975 casts: term -21 This inventionrelates to duo-mode wave energy feeds and 'niore particularly to" a wave energy transducer which provides waveenergy in a combination of the principal T E-M=mode' and the higher" TE b mode of a coaxial waveg e. t U

In certain applications; waveenergy antenna systems filayltb called upon to radiate'a cross-polarized beam of wave energy. The'antenna of such a system is adapted to'receiveaandto radiateiwave energypolarized win two mutually .perpendicular iplanes. The feed means used in conjunctionwith such an antenna :must likewise be adapted toexcite andbe excited" bywave energy polarizedain ttwo mutually/"perpendicular planes. An adequate feedfnieans.risi onetcadapted to excite wave energy in two modes having their .respectiverelectric field. vectors atright angles to one another. t An :example Of? an: antenna zadapted to. radiate and receiveirdrthogonally polarized wave energy is an omnidirectionalh surface". wave 'beaon antenna having a .dielectricrclad tmetallic'asurface the dielectric being utilized asaztrapping agentrthe dielectric is of the multiple slab itype,it may be 'adaptedl'to propagate the orthogonal surfaceswavecomponents with the. sameavelocity. To utilize, the I. properties of-this antenna, a coaxial waveguideffeedis used, to, supply the composite dielectric trapping agent with elliptically polarized wave energy of high power." One way to ob tain the desired cross components-of waveenergyis to excite wave energy in the coaxial feed waveguide in two modes,-namely -tthe TEM- mode and the TE -mode.

lt isdtherefore an object of this invention to provide a-wave fenergy feed whichis adapted to excite wave energy in a..combination of the TEM-mode and the TE -mode of a coaxialwwaveguide at its output end.

.,It is a-. further object of this invention to provide. a device which, upon being, excited with'wave. energy in the dominant TEM-mode of a rectangular waveguide, directlyj transforrns a predetermined and adjustable portion ofthe energy of the excited mode into the TE mode of a coaxial waveguide and directly transforms the remaining energy portion of the excited mode into the TEM-modeof a coaxial waveguide. "I'tis another object ofythis invention to provide a new and novel duo-mode wave energy feed capable of providing wave" energy in an easily adjustable proportion of the TEM and TE -modes of .the coaxial waveguide without the employment of interposed excitation elements which feed is simple in operation and capable of handling large amounts of power. t

1n accordancewtih this invention, wave energy propagated; along a rectangular waveguide in the dominant TE -mode is divided into two equal portions in such a manner that the electric field vectors of the two divided portions are colin ear. The electric field vector of each of 'the two portions of wave energy is then rotated so thatfthe direction of linear polarization of the two porf'tionssuffe'rsan angular displacement through an angle pffq degrees' 19-3 189 degrees, respectively, This rotation leaves the electric field vectors of the two divided portions parallel and opposite to one another; Thereafter, the two portions of wave energy are recombined such that the components of the angularly displaced electric fieldvectors along. the original direotion of linear polarization will. combine to provide the TEM- mode of a coaxial. waveguide,. and the-components of the angularly displaced electric'fieldalong-a direction perpendicular to the original direction of linear polarization will combine to provide the higher TE -mode of a coaxial waveguide. The ratio of theenergies divided between the two modes is proportional to the.=angle6.uso that control of the rotationofthe. electric-field vector controls the relaitve amountsof the energy in theresult-i ing modes. 1

The novel features which are believed to be charactcre istic of the invention, both as to its organization and method of operation, together with further objectstand advantages thereof, will be better understood from tthe following description considered in connection withthe accompanying drawing in which an embodiment of the invention is illustrated byway of example. It.is.:to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention'.

Fig. 1 is afragmentary perspective view of an embodi: ment of the duom0de wave energyfeed of this invention; and .1. Rm.

Figs. 2 to 7 are cross-sectional perspectivedviews of different portions of the duo-mode feed of Fig. 11: show ing the progressive reorientation of the electric field vector or vectors E. 9 Referring now to the drawing and particularly toFig. 1-there-is shown a duo-mode wave energyfeed 10 ,in accordance with this invention. For the purposeofthe specification and to facilitate the description of thewwave energy feed of the invention, the device 10* is considered as being made up of a dividing section '12, a rotating section 14 and a recombining section 16. Such division is arbitrary and does not designate physical entities whichare coupled to one another.

The dividing section 12 is essentially a Y-type power divider comprising a standard rectangular waveguide 18 which. separates to provide a pair of identical branch waveguides 20 and 22. Thebranch waveguides 20 and 22 may also be standard rectangular waveguides as shown. The end of the branch waveguides 20 and 22 are equipped respectively with tapered or fia red end porjtions 24 and 26 to effect a smooth transition to a pair of square waveguides. One of the branch waveguides is further provided with a 180 degrees phase-shift means such as a dielectric plate 28 here shown inserted into waveguide 22 which is adapted to change the electric path length by one-half of the working wavelength from that of the physical path length. It will be obvious to those skilled in the art that the dielectric plate 28 is just one of many means of affecting the desired pathlength and that choke sections, twisted waveguides, folded wave guides and certain dielectric plugs subjected to magnetic orelectric fields may be substituted therefor. t

The ultimate purpose of the dividing section 12 is to receive wave energy in the dominant TE -mode of a rectangular waveguide and to provide to the rotating section 14 as a source the received wave energy divided into two substantially equal portions having a relative phase shift of 180 degrees therebetween. Therefore a Y-type power divider whose branch arms are each twisted through an angle of degrees or a Magic Tee whose symmetry arms are each. twisted through an angle of 90 degrees, may be substituted for the dividing section12 hereabove described. v The rotating section 14 of the wave energy feed 1Q comprises a pair of identical square waveguides 30 and 32, each one of which is coupled to a different one of the tapered end portions 24 and 26 of the dividing section 12.-and capable of supporting cross-polarized wave en ergy. Each of the waveguides 36 and 32 is provided with wave energy rotating means 34 and 36 adapted to rotate the plane of polarization of the wave energy passing therethrough. Wave energy rotating means are well known in the art and are illustrated by way of example to comprise a pair of elongated ferromagnetic ceramic pencils 38 and 40 axially positioned within the respective waveguides 30 and 32. These ferromagnetic ceramic pencils may be supported by polystyrene supports 41, 42, 43 and 44 respectively.

Surrounding the pair of square waveguides 30 and 32 is an electromagnet 46 connected to a battery 48. The current through the electromagnet 46 may be adjusted by means of a resistance R put in series with lead 49 and a sliding contact 50. The magnitude of the current passing through the electromagnet 46 determines the magnitude of the axial magnetic field produced. As is well known in the art, ferromagnetic ceramic elements subjected to a steady axial magnetic field exhibit the Faraday effect which produces antireciprocal rotation of the plane of polarization. The extent of rotation suffered by the Wave energy passing through the pencils 34 and 36 is directly proportional to the magnitude of the magnetic field and the physical characteristics of the pencils 3% and 40. It therefore follows that motion of the sliding contact 50 changes the current flow through the electromagnet 46 which in turn results in a change of the angular displacement of the plane of polarization. Many other materials exhibit charactertistics similar to these of ferromagnetic ceramic substances and may be substituted therefor.

The recombining section 16 of the Wave energy feed is essentially a waveguide transition from an oversized rectangular waveguide partitioned by the pair of thin conducting walls 52 and 53 of the square waveguides 30 and 32 to a coaxial waveguide 56 having an outer conductor 58 and an inner conductor 60. The outer conductor 58 progressively changes in cross-section from that of the over-sized rectangular waveguide to that of a uniform cylindrical outer conductor 62 of the coaxial waveguide 56. The thin conducting walls 52 and 53 which extend into the recombining section 16 merge to form the inner conductor 60 and are disconnected from the outer conductor 58 at the point 64. Thereafter the merged walls gradually taper in width towards the center line of the coaxial waveguide 56 until their cross-section becomes circular.

Figs. 2-7 are cross-sectional perspective views taken along the various lines 2-2 to 77 taken along the wave energy feed of Fig. l and have been included to aid in the explanation of operation of this invention.

Wave energy in the TE -mode enters the dividing section 12 of the wave energy feed 16 through the rectangular waveguide 18. Fig. 2 shows the vertical orientation of the electric field vector E. The (-type power divider which feeds the pair of branch Waveguides 2t and 22 splits up the wave energy from the waveguide 1'8 into two substantially equal portions. Fig. 3 shows the wave energy split into two equal portions whose respective electric field vectors E are colinear. As wave energy traverses the branch waveguide 22 it encounters the 180 degrees phase shift means 28 which changes the physical path length by one-half of the working wavelength. Fig. 4 shows relative phase relations between the electric field vectors of the two energy portions after one portion has suffered traversal through the 180 degrees phase shift means.

As wave energy is propagated through the rotating section 14 of the wave energy feed 10, the direction of linearpolarization or, which is the same, the electric field vector E' of the wave energy passing through each of the rotators 34 and 36 is rotated through the same angle. As mentioned above, the angular displacement of the linear polarization is determined by the strength of the current passing through the electromagnet 46. Fig. 5 shows the position of the rotated electric field vectors. Fig. 5 also shows the components of the electric vectors E along lines parallel to the walls of the square waveguides. These components are designated respectively as E and B As can readily be seen from the drawing, related E components are colinear and 180 degrees out of phase with one another and related E components are parallel and also 180 degrees out of phase with one another.

Upon traversing the recombining section 16, the Wave energies of the two portions are recombined so that the E components provide the TEM-mode of a coaxial waveguide whereas the E components provide the TE -mode of a coaxial waveguide. Fig. 6 shows one single sequence in the progressive reorientation of the electric field vector components E and E resulting in the gradual formation of the desired output modes. Fig. 7 illustrates the TEM-mode and the TE -mode of a coaxial waveguide which is the output of the wave energy feed 10.

As is readily seen from the foregoing description of the operation of the wave energy feed of the invention, the electric field generated by the electromagnet 46 will determine the energy ratio of the two output modes. At all times the sum of the energies of the two modes is equal to the input energy. If the magnetic field is zero and no rotation of the plane of polarization of the wave energy traveling through the rotators 34 and 36 takes place, the E component of wave energy is zero and consequently all wave energy will appear at the output in the TEM-mode. Similarly if the current in the electromagnet is adjusted to produce a magnetic field of such a strength that the linear polarization of the wave energy passing through the rotators 34 and 36 suffer a degrees rotation, the E component of thewave energy is zero and consequently the only'output mode at the end of the coaxial waveguide 56 is the TE -mode. By adjustment of the magnetic field, the desired energy ratio of the TEM-mode and the TE -mode may be obtained.

For best operation of the Wave energy feed 10 it has been found desirable to use identical rotators 34 and 36 so that upon recombination, the amount of distortion of the two portions of wave energy will be equal. The device It will also work if the respective rotators 34 and 36 produce unequal rotation but higher modes will be generated thereby. The degrees phase-shift means which has been shown to be located in the branch waveguide 22 may be placed in the square waveguide 32 as appears obvious from the function to be performed.

Elliptically and circularly polarized wave energy is obtainable in an antenna coupled to the feed of this invention by using a length of coaxial line which provides a 90 degrees relative phase shift between the two modes. As is well known, wave energy in the TEM- mode will be propagated through a coaxial waveguide at a different velocity than the TE -mode. Accordingly, it is only necessary to find a length of coaxial waveguide at which the desired phase shift exists.

What is claimed is:

l. A duo-mode wave energy feed adapted to effect a unity transition between the dominant TE -mode of a rectangular waveguide and a predetermined energy ratio of the principal TEM-mode and higher TE -mode of a coaxial waveguide, said feed comprising in combination: waveguide dividing means for equally dividing wave energy in the dominant TE -mode of a rectangular waveguide into two portions having co-linearly disposed electric field vectors, said dividing means including phase shifting means to provide a 180 degrees phase differential between said two portions; rotating means coupled to said dividing means for separately rotating the plane of polarization of each of said two portions of wave energy through a predetermined angular displacement; and combining means coupled to said rotating means for combining said two rotated portions of wave energy to provide said principal TEM-mode and said higher TE mode of a coaxial waveguide.

2. A duo-mode wave energy feed adapted to efliect a unity transition between the dominant TE -mode of a rectangular waveguide and a predetermined energy ratio of the principal TEM-mode and higher TE -mode of a coaxial waveguide, the energy ratio being adjustable, said feed comprising in combination: dividing means for equally dividing wave energy in the dominant TE -mode .of a rectangular waveguide into two portions; rotating means coupled to said dividing means for separately rotating the plane of polarization of each of said two portions of wave energy through a predetermined angular displacement of the same screw sense, said rotating means including two separate ferrite pencils within two separate waveguides subjected to a substantially identical adjustable magnetic field for changing the magnitude of said predetermined angular displacement; phase-shift means coupled to said feed and adapted to provide a relative phase shift of 180 degrees between said two portions of wave energy; and combining means coupled to said rotating means for combining said two rotated and phase shifted portions of wave energy to provide said principal TEM-mode and said higher TE -mode of a coaxial waveguide.

3. A duo-mode wave energy feed adapted to eifect a unity transition between the dominant TE -mode of a rectangular waveguide and a predetermined energy ratio of the principal TEM-mode and higher TE -mode of a coaxial waveguide, the ratio of said combination being changeable, said feed comprising in combination: dividing means for equally dividing wave energy in the dominant TE -mode of a rectangular waveguide into two portions having co-linearly disposed electric field vectors, said dividing means including phase shifting means to provide a 180 degrees phase differential between said two portions; rotating means coupled to said dividing means and including a pair of waveguides defining wave energy propagation paths, each waveguide having an elongated ferromagnetic ceramic body axially located therein, said rotating means also including electromagnetic field means adapted to provide a magnetic field passing axially through each of said bodies, and adjustment means included in said field means to vary the magnitude of said magnetic field, said rotating means imparting an angular displacement to the plane of polarization of each of said two portions of wave energy; and combining means coupled to said rotating means for combining said two portions of wave energy to provide said principal TEM- mode and said higher TE -mode of a coaxial waveguide.

4. A duo-mode wave energy feed comprising: a rectangular input Y-type power divider having two output waveguides capable of supporting energy in various positions of rotation, means included within said output waveguides to provide 180 degrees relative phase shift between respective wave energy propagated therethrough, two elongated ferromagnetic ceramic elements, each of said output waveguides being provided with one of said ceramic elements; electromagnetic field means adapted to provide a magnetic field passing axially through each of said ceramic elements, and adjustment means included within said field means to vary the strength of said magnetic field, said output waveguides being disposed in parallel relationship having corresponding walls disposed adjacent in parallel relationship, the walls separating said output waveguides merging with one another to form a merged wall, said merged Wall being detached from the remaining waveguide walls and being progressively tapered in width to form the center conductor of a coaxial waveguide, the remaining walls of said output waveguides being combined to form a rectangular waveguide whose cross-section progressively changes along its length into a cylindrical waveguide to form the outerc'onduc'tor of said coaxial waveguide.

S. A duo-mode wave energy feed adapted to eflect a unity transition between the dominant TE -mode of the rectangular waveguide and a continuously adjustable energy ratio of the principal TEM-mode and higher TE -mode of a coaxial waveguide comprising: dividing means responsive to wave energy in the dominant TE mode of a rectangular waveguide and adapted to equally divide said dominant TEm-mode into two portions, said dividing means including phase shift means adapted to impart a degrees phase differential between said por tions; rotating means responsive to said two portions of wave energy and adapted to separatelyrotate each 'of said two portions of wave energy through a substantially identical predetermined angular displacement; and com bining means, said combining means including an outer member having a substantially rectangular input section and a substantially circular output section and whose cross-sectional shape changes progressively from rectangular to circular cross-section, said combining means further including a conductive wall across said input section dividing said input section into two substantially equal square waveguide portions, each of said two square waveguide portions being coupled to said rotating means for receiving a different one of said rotated portions of wave energy, said conductive wall being separated from said outer member and progressively tapering in width to wards its center-line to provide the center of a coaxial waveguide forming said output section of said combining means.

6. A duo-mode wave energy feed adapted to effect a unity transition between the dominant TE -mode of a rectangular waveguide and an energy ratio of the principal TEM-mode and higher TE -mode of a coaxial waveguide, the energy ratio being adjustable, said feed comprising in combination: a rectangular waveguide Y-type power divider having two output ports, two square waveguide sections, each being coupled to a difierent output port of said divider, phase shift means included within said square waveguide sections and adapted to provide 180 degrees relative phase shift between wave energy propagated by said two square waveguide sections; two elongated ferromagnetic ceramic elements, said square waveguide sections each being provided with one of said ceramic elements, electromagnetic field means coupled to said square waveguide sections and adapted to provide a magnetic field passing axially through each of said ceramic elements, adjustment means included in said field means to vary the strength of said magnetic field; and a rectangular-tocoaxial waveguide transition, said transition including an outer member having a substantially rectangular input section and a substantially circular output section and whose cross-sectional shape changes progressively from rectangular to circular crosssection, said transition also including a conductive wall across its'input section dividing said input section into two equal square waveguide portions, said two square waveguide sections being coupled to said two square waveguide portions, said conductive wall being separated from the outer member and progressively tapering in width towards its center line to provide the center conductor of a coaxial waveguide forming the output section of said transition.

7. A duo-mode wave energy feed adapted to effect a unity transition between the dominant TE -mode of a rectangular waveguide and a predetermined energy ratio of the principal TEM-mode and higher TE -mode of a coaxial waveguide, the ratio of said combination being changeable, said feed comprising in combination: dividing means for equally dividing wave energy in the dominant TE -mode of a rectangular waveguide into two portions, said dividing means including phase shifting means to provide a 180 degree phase differential between 7 said two portions; rotating means coupled to said dividing means and including a pair of waveguides defining wave energy propagation paths, each Waveguide having an elongated ferromagnetic ceramic body axially located therein, said rotating means also including electromagnetic field means adapted to provide a magnetic field passing axially through each of said bodies and adjustment means included in said field means to vary the magnitude of said magnetic field, said rotating means iraparting an angular displacement to the plane of polarization of each of said portions of wave ener and combining means coupled to said rotating means for co 1.- bining said two portions of wave energy to provide said principal TEMmode and said higher TE -mode of a coaxial waveguide, said combining means including two output waveguides disposed in parallel relationship having contiguous walls, said contiguous walls merging with one another to form a merged wall, said merged wall being detached from the remaining waveguide Walls and being progressively tapered in Width to form the center conductor of a coaxial waveguide, the remaining walls of said output waveguides being combined to form a rectangular waveguide whose cross-section progressively changes along its length into a cylindrical waveguide to form the outer conductor of said coaxial waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,129,669 Bowen Sept. 13, 1938 2,439,285 Clapp Apr. 6, 1948 2,555,118 Coyle et al. a. May 29, 195 2,636,083 Phillips et al. Apr. 21, 1953 2,644,930 Luhrs et al. July 7, 1953 2,656,513 King Oct. 20, 1953 2,809,354 Allen Oct. 8, 1957 2,818,501 Stavis Dec. 31, 1957 2,839,729 Gibson July 17, 1958 

